The present invention relates to an antenna used wireless communication system, in particular, relates to a multi sector antenna having a plurality of element antennas so that a single beam in desired direction is radiated and the direction of a beam may be switched by selecting one of the element antennas
FIG. 11 shows a top view of a prior multi sector antenna, in which the numerals 1a through if are an element antenna, 2a through 2f are a beam radiated by the related element antenna In a prior multi sector antenna as shown in FIG. 11, assuming that it has N number of element antennas (N=6 in the embodiment of FIG. 11), the external diameter D of the multi sector antenna, or the longest length D of the multi sector antenna in horizontal plane, is expressed as follows, where d is the horizontal length of each element antenna, and cross over level is -3 dB. EQU D.apprxeq.d/(sin(180.degree./N)) (1)
The number N is usually equal to or larger than 3.
It should be noted in the equation (1) that the external diameter D is increased when the number N of the element antennas is large
Therefore, the prior multi sector antenna as shown in FIG. 11 has the disadvantage that the external diameter D is extremely large when the number N of the sectors (or element antennas) is large.